The invention is a radiant energy collection device. More specifically, the invention is a roll based radiant energy collection and measuring device for use in a process line.
Processing systems using radiant energy sources are known in many industrial processes. One exemplary processing system uses ultraviolet (UV) lamps or bulbs placed near a product in a manufacturing line to cause chemical reactions to occur in or on the product. Often these chemical reactions are referred to as curing (or in some industries as drying). The wavelengths of radiant energy radiated by UV lamps in both the visible and the non-visible spectrum have been found to be particularly effective in transferring energy to the product to effect the desired chemical changes.
The energy wavelengths radiated onto the product typically range from approximately 2.5 micrometers to approximately 190 nanometers. The product being processed by the system can be almost anything, but typically it is a “web” of paper, plastic, or paper-like material (e.g., paperboard). The “web” comprises a continuous stream of material fed through a series of rollers. Radiant energy sources (typically more than one lamp or bulb) are placed at various points along the web to radiate energy onto the web. One or more coatings on the surface of the web, or the web material itself, are caused to undergo a chemical change during this process. In this manner the coating on the web (e.g., ink, lacquer, or adhesives) or the web itself is cured.
Unfortunately, the performance of an individual UV energy lamp (or any other energy source) can vary. A newer lamp may radiate energy more intensely than when it is older. Individual lamps with the same specifications can perform differently. Individual lamps may also perform differently along their length. Specifically, different wavelengths may be emitted more intensely from one lamp to the next. As would be expected, as a lamp grows older, its performance typically declines until it ultimately fails. The power provided to the lamp can also affect the lamp performance. If the electrical service to the lamp fluctuates, specific wavelengths produced by the lamp may vary in intensity. Differences in air temperature surrounding the lamp as well as the time it takes for the lamp to warm up may also cause fluctuations in wavelength intensity. All these variances in the intensity of the radiant energy emitted by the lamp can cause the level of curing of the web to vary. Therefore, in order to optimize the process and provide consistent product it is necessary to monitor the amount of radiant energy emitted by the lamp in order to assure proper curing (i.e., radiation exposure as a function of intensity and exposure time) of the web.
To measure the amount (or “dose”) of radiant energy impinging on the web, a detection system is needed. One previous method to evaluate whether the source was providing adequate radiant energy was to test the web downstream from the lamp. Although this gave a very accurate measurement of whether the web had been properly cured, the measurement took place too late in the process, since product which had not been properly cured could not be used, and was thus discarded.
An alternate measurement method was to use electronic devices such as compact integrating radiometers (known in the art) placed on the web and moved with the web between the lamp and the web to provide a test measurement of the amount of radiant energy being emitted by the lamps. While this method gave a more direct measurement of lamp performance, it was performed during setup and not during actual production so that no information was being gathered as to energy impinging the web during the actual run time process. In particular, no measurements of variances in the radiant energy impinging the web were able to be taken. Once again, improperly cured product resulted. Additionally, passing the web through nip points and idler rolls, as is required in some casting processes, could damage the compact integrating radiometers before measurements could be obtained.
Another alternative method was to use actinometric devices to measure the amount of radiation. An actinometric device's chemical composition changes as it is exposed to radiation. Examples of actinometric devices are tapes or films embedded with a substance that changes color in response to radiation. Although these devices can pass through nips, they must be manually placed on the web to expose them to radiation, and manually removed to obtain a reading. They are not continuous measures of radiation in a process.
Another method was developed which monitored the energy draw of the power supply for each lamp, in an attempt to provide a “real time” measurement of the actual energy used by the lamp. This measurement was a very rough and inaccurate way to estimate the amount of radiant energy emitted by the lamp and impinging on the web on a continuous basis. Although inaccurate, this method was an attempt to determine how much radiant energy was impinging onto the web in “real time”. Measuring the radiant energy in “real time” made it possible to more accurately control the curing time of the web (e.g., by changing the pace of the web through the process to provide longer or shorter processing time) and reduce loss of product. Unfortunately, many factors made the measurement of the energy drawn from the lamp an inaccurate measurement of the radiant energy impinging the web defeating any advantages gained by the real time measurements. For example, as the lamps themselves degraded due to aging, the amount of energy drawn by the lamp could change relative to the amount of radiation emitted. Additionally, the radiation emitted for a specific amount of power drawn varied from lamp to lamp. To alleviate these problems, electronic detection devices were placed around the lamp to measure the direct output of radiant energy emitted from the lamp. However, the environmental conditions surrounding the process (e.g., high humidity, high temperature, RF radiation, and foreign objects such as airborne adhesive, lacquer, etc.) often caused the electronics in the detectors to break down and malfunction.
Finally, remote collection devices have been developed which allow the radiant energy emitted by the lamp to be collected and transported (typically by fiber optic cables) to a detection device placed remotely from the hostile environment surrounding the web. These devices were placed on the backside of the lamp (opposite the web), allowing a direct measurement of the amount of radiant energy emitted by the lamp to be taken. This placement of these devices on the opposite side of the lamp from the web was done for two main reasons: first, there was very little space between the web and the lamp and second, because the most hostile environment in the process is directly between the web stream and the surface of the lamp housing. The space between the web and the lamp was small in order to keep contaminants such as oxygen (which can affect curing of the web in some processes) to a minimum, as well as assuring that a maximum amount of radiant energy from the lamps impinged the web. The environment is extremely hostile at this position since it is most directly in contact with the radiation and heat from the lamp as well as the adhesive and airborne contaminants from the web.
While remote collection devices solved some of the problems described above, they still did not deliver accurate measurements of radiant energy intensity impinging the web. Typically, a transparent cover is placed over the lamp in order to protect the lamp elements from airborne contaminants. This transparent cover becomes clouded over time (due to airborne contaminants), which prevents a portion of the radiant energy emitted by the lamp from impinging upon the web. Thus, collection devices placed at the back of the lamp do not see this degradation, and an accurate measurement of energy radiated onto the web cannot be attained. None of the devices allowed for the real time collection of radiant energy at the web.